The present invention relates to an improved method of coupling optical waveguides together.
Optical waveguides technology, such as optical fibers for the transmission of information-bearing light signals, is now an established art. The fiber optic technology has found widespread application in the telecommunications, medical, and electronic industries. Much developmental work has been devoted to providing optical fibers of materials that lose only low levels of light. In order to take full advantage of the development of such low-loss materials in the fiber optic industry, practical connections must be provided so that the optical fibers may be easily coupled to each other. The ease of mechanical connection and the amount of transmitted light lost in the connection because of reflection, misalignment, or fiber surface effects are prime concerns in the design of a connector for optical fibers. These connections should allow the optical fibers to be reversibly coupled to each other so that repeated connections may be made between distinct optical fibers lengths. Also, the connections must provide an optical pathway between distinct optical fibers that allows the transmission of light from one optical fiber to another without reflection back along the fiber axis. For reasons well established in the art, it is desirable that the optical pathway include materials that have an index of refraction substantially equal to the index of refraction of the optical fibers.
Several methods are known for coupling optical fibers together; for instance, it is known that epoxy resins may be used to permanently adhere one optical fiber to another optical fiber. The epoxy resin is normally chosen so that the index of refraction of the epoxy resin is close to the index of refraction of the optical fiber, thus minimizing the reflection of light back along the fiber axis as the transmitted light passes through materials having a different index of refraction. Another method of coupling optical fibers uses a coupling gel that is placed in the interface between adjacent optical fibers. The index of refraction of the coupling gels preferably matches the index of refraction of the optical fibers and provides a medium through which the transmitted light passes from one optical fiber to the other optical fiber. Coupling gels, however, are generally viscous materials that tend to flow out or be squeezed out of the interface between the adjacent optical fibers and therefore do not lend themselves to repeated connections. Also, coupling gels are generally prepared from materials that tend to absorb moisture over time, thus resulting in an unpredictable change in the index of refraction of the coupling gel.
U.S. Pat. No. 3,914,015 to McCartney reports a transparent interface component that has an index of refraction consistent with the index of refraction of a plurality of optical fibers to be coupled. The transparent interface component is structurally independent of each of the plurality of optical fibers that are coupled together. The component appears to be held in position by the compressive forces supplied by the optical fibers and the alignment sleeves surrounding the optical fibers.
U.S. Pat. No. 3,910,678 to McCartney et al. provides an annular-shaped sleeve of a transparent optical interface material that occupies the interface between a first plurality of optical fibers to be connected to a second plurality of optical fibers. The transparent interface is held in place by an alignment sleeve that surrounds the transparent interface and the optical fibers. The transparent interface is structurally independent of both the first and second plurality of optical fibers. In both the '015 and '678 patents, the index of refraction of the transparent interface is consistent with the index of the refraction of the optical fibers to be coupled to each other.
The use of structurally independent transparent interfaces between optical fibers to be coupled to each other suffers from the drawback that the compressive or shearing forces encountered between the interface and the fibers when aligning and connecting the optical fibers may result in substantial damage to the terminal ends of the optical fibers. Any damage that occurs to the ends of the optical fibers can result in a substantial increase in the amount of light reflected back along the axis of the fiber or the amount scattered at the interface. Also, the structurally independent transparent interface must be independently fabricated to predetermined dimensional tolerances in order to cooperate with the alignment sleeve.